Developments in zeolite catalysis and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks for producing C.sub.5.sup.+ gasoline, diesel fuel, etc. In addition to basic chemical reactions promoted by ZSM-5 type zeolite catalysts, a number of discoveries have contributed to the development of new industrial processes. These are significantly safe, environmentally acceptable processes for utilizing feedstocks that contain lower olefins, especially C.sub.2 -C.sub.5 alkenes. In U.S. Pat. Nos. 3,960,978 and 4,021,502, Plank, Rosinski and Givens disclose conversion of C.sub.2 -C.sub.5 olefins, alone or in admixture with paraffinic components, into higher hydrocarbons over crystalline zeolites having controlled acidity. Garwood, et al., have also contributed improved processing techniques, as in U.S. Pat. Nos. 4,150,062, 4,211,640 and 4,227,992. The above-identified disclosures are incorporated herein by reference.
Conversion of lower olefins, especially propene and butenes, over HZSM-5 is effective at moderately elevated temperatures and pressures. The conversion products are sought as liquid fuels, especially the C.sub.5.sup.+ aliphatic and aromatic hydrocarbons. Product distribution for liquid hydrocarbons can be varied by controlling process conditions, such as temperature, pressure and space velocity. Gasoline (C.sub.5 -C.sub.9) is readily formed at elevated temperature (e.g., up to about 400.degree. C.) and moderate pressure from ambient to about 5500 kPa, preferably about 250 to 2900 kPa. Olefinic gasoline can be produced in good yield and may be recovered as a product or fed to a low severity, high pressure reactor system for further conversion to heavier distillate-range products. Distillate mode operation can be employed to maximize production of C.sub.10.sup.+ aliphatics by reacting the lower and intermediate olefins at high pressure and moderate temperature. Operating details for typical "MOGD" oligomerization units are disclosed in U.S. Pat. Nos. 4,456,779; 4,497,968 (Owen, et al.) and U.S. Pat. No. 4,433,185 (Tabak), incorporated herein by reference. At moderate temperature and relatively high pressure, the conversion conditions favor distillate-range product having a normal boiling point of at least 165.degree. C. (330.degree. F.). Lower olefinic feedstocks containing C.sub.2 -C.sub.6 alkenes may be converted selectively; however, the low severity distillate mode conditions do not convert a major fraction of ethene. While propene, butene-1, and others may be converted to the extent of 50% to 95% in the moderate temperature distillate mode, only about 10% to 30% of the ethene component will be converted using HZSM-5 or similar acid zeolites. Many feedstocks of commercial interest, such as FCC offgas, dehydrogenation products, ethane cracking, etc., contain both ethene and hydrogen along with H.sub.2 S and light aliphatics. Ethene can be converted at moderately elevated temperature with a bifunctional nickel zeolite catalyst. However, it has been found that the presence of reducing gas in the feedstock would inactivate the nickel oligomerization component, thus decreasing the yield of C.sub.3.sup.+ hydrocarbon products.